Dana Boente, who was U.S. attorney for the Eastern District of Virginia, was heavily involved in the transition at the Justice Department as the Trump administration was transitioning in . ( Mark Wilson/Getty Images file photo)

Sen. Chris Coons has questions for the Justice Department after the pending forced resignation of a top U.S. attorney who played a pivotal role early in the Trump administration and initial probes into the ties between the president's campaign and Russia.

Dana Boente, the U.S. Attorney for the important Eastern District of Virginia, was asked to quit in late October by attorney general Jeff Sessions.

He tendered his resignation three days before Special Counsel Robert Mueller indicted former Trump campaign chairman Paul Manafort and two other former Trump aides, charges that arose from Mueller’s investigation into ties between the Trump campaign and Russia.

Coons, a Democratic Senate Judiciary member from Delaware, is writing a letter to top Justice officials to ask if Boente’s resignation was “normal or justified,” he told Reuters.

“I’m concerned about the abrupt departure of Dana Boente after a career as a federal prosecutor,” Coons said. “There’s a lot of circumstances that connect the ongoing Mueller investigation to the Eastern District.”

Watch: What’s Congress’ Role in the Russia Investigation? One Senator Explains

Boente was instrumental in helping the Trump administration’s roiling Justice Department transition into the hands of the president’s nominees.

He became the acting attorney general after the president fired Sally Yates from that post in January. When Sessions took over as Trump’s appointed AG, Boente served as acting deputy AG until Rod Rosenstein was confirmed in April. Most recently he was filling a vacancy as acting assistant attorney general for the department’s National Security Division.

He is being phased out of the Justice Department entirely once the Senate confirms Trump's nomination for his post in Eastern Virginia.

That district is where federal investigators received a warrant to search Manafort's home in July.

Correction 6:11 p.m. | An earlier version of this story incorrectly detailed the succession of interim positions U.S. Attorney Dana Boente held over the last year as President Donald Trump fleshed out his Justice Department. It also incorrectly stated Boente had resigned from his current post. He has tendered his resignation, effective upon the confirmation of a new U.S. Attorney in the Eastern Virginia District. The story has been updated to reflect these changes.